1. Field of the Invention
The present invention relates to a dielectric ceramic composition having a high dielectric constant and a small temperature dependence thereof, and particularly to a composition adapted to a multi layered ceramic capacitor (MLCC) having a large capacitance.
2. Description of the Prior Art
The dielectric ceramic material composed of BaTiO.sub.3 as a main component has heretofore been used for MLCC which, however, has recently been replaced by a new dielectric ceramic material, i.e., replaced by a composition of Pb(FeNdNb)O.sub.3 having a perovskite structure that can be fired at a low temperature and has a large dielectric constant (Japanese Laid-Open Patent Publication No. 216106/1987). This dielectric ceramic material allows the use of a cheaply available silver-palladium type of electrode material for firing at low temperatures instead of using expensive Pd that was used so far, makes it possible to roughly double the dielectric constant compared with the case of using a material which is chiefly composed of BaTiO.sub.3 and, hence, makes it possible to increase the capacitance and, further, to decrease the number of dielectric layers if the same capacitance is to be obtained enabling the size to be reduced.
The above-mentioned conventional dielectric ceramic material exhibits a dielectric constant that greatly changes depending upon the temperature; e.g., the dielectric constant changes over a temperature range of, for example, from -30.degree. C. to 85.degree. C. by as greatly as +15% to -75% compared with the dielectric constant at room temperature. That is, the dielectric ceramic material exhibits properties that are inferior to those of the generally used tantalum electrolytic capacitors placed in the market of large-capacitance capacitors, and poses a bottleneck against being put into practical use.
The object of the present invention therefore is to provide a dielectric ceramic composition which exhibits a high dielectric constant that varies little depending upon the temperature, and has a high mechanical strength.